Cleaner, greener buses

Thanks to some cleaner buses that are about to hit the streets of Austin we can all breathe a little easier. Capital Metro is putting the finishing touches on eight new clean diesel buses that meet the new 2010 standards by the Environmental Protection Agency.

The new buses give off 0.2 gram per brake horsepower hour (g/bhp-hr) of nitrogen oxides (NOx) and 0.01 g/bhp-hr of particulate matter (PM). So what does that mean? Well, it means these buses are 25 times cleaner than buses from 20 years ago and 10 times cleaner from just last year!

The new 35-ft buses are manufactured by New Flyer and have Cummins ISL engines. They can hold 28 seated passengers and 2 wheelchairs. Each bus is equipped with security cameras.

The new buses will be replacing buses that are 13 years old. Next year, we’re looking at replacing around 25 more buses.

5 thoughts on “Cleaner, greener buses”

The standard for clean-diesel buses is listed in a peculiar form (gram per brake horsepower hour) that is not used for cars, which makes the comparison more difficult than it might seem at first glance.
Comparisons of environmental effects of different modes is challenging. There is a recent TCRP Synthesis paper #84- Current Practices in Greenhouse Gas Emissions Savings from Transit. On p. 14:
“A research team at the University of California, Berkeley,
conducted an extensive analysis of GHG emissions from each life-cycle component of auto, bus, light-rail, and heavy-rail transportation. Figure 8 shows the relative life-cycle impacts of cars, SUVs, pickups, and buses, as calculated in that study. A typical bus running during peak hours, with 40 passengers, has the lowest emissions per passenger mile traveled. A typical bus running during off-peak hours, with only five passengers, has the highest emissions of GHGs per passenger mile traveled. The study assumed average passenger loads of 1.58 for sedans, 1.74 for SUVs, and 1.46 for pickups.”

GHG is only one pollutant – you also have to talk about particulates, NO2, etc. And even clean diesel in cars is far dirtier than their corresponding gasoline engines – clean diesel in buses is going to produce far more of that bad stuff.

With the new bus engine technology, the whole bus v. car environmental comparison is (generally) more dependent on how full the bus is than on what the fuel is.

The reason I cited the life-cycle reference is that any real environmental impact comparison needs to look at the whole picture, including the well-to-wheels piece, not just the pollutants-per-gallon piece.

The environmental impact of transportation is (I think) fascinating and complex, with new research coming all the time, so there is plenty of room for learning and getting better!

I am sure that I don’t know the latest on all this, but I try to keep up with some of it, so did have the TCRP report handy.

Like most such pieces, the piece you reference talks a lot about how much cleaner the new diesel engines are than old diesel engines but curiously fails to mention how clean a ‘clean diesel’ engine is compared to a modern gasoline engine. There’s a reason for that.